Beyond the Limits Workbook

In this workbook, you will learn about key ideas
and findings of the book Beyond the Limits.

For this workbook, you will need the Macintosh
computer program about Beyond the Limits.


















About This Workbook

This workbook is intended to convey key ideas from Beyond the Limits. It asks you to think through some possible consequences of human population and industrial growth. In the process, you will think about some ways to help build a better future.

The workbook is divided into sections. Classes may find it practical to do about one section per day of class. Please, discuss your work with friends, classmates, and teachers--both while you use the workbook, and afterwards.

If you are learning on your own about Beyond the Limits, this workbook should be a useful guide. Note especially question 7, which helps you learn to use the Beyond the Limits computer program.

This workbook has not been tested to evaluate its educational impact. Feel free to pick and choose among the parts of the workbook, or use it as a source of ideas. And of course, please send your comments and suggestions!


Sections of the Workbook

Back to main document about Beyond the Limits.


State of the World

You ought to know what has been happening in the world before you think about what will happen. So before you use the rest of this workbook, take time to read about how the world's population, industry, agriculture, pollution, and resource use have changed over the 1900s. Don't bother to memorize lots of facts. Just learn the general trends, and learn where to look up this information.

One way to learn this is to read chapters 1-3 of the book Beyond the Limits. A shorter summary appears in the computer program and in the Beyond the Limits Reader on the World Wide Web. (In the "Learn about Beyond the Limits" section, see "The World Today.") Or use books such as World Resources and World Development Report.

Back to contents.


Potential Limits to Growth and What to Do about Them

The world's population has been growing ever-faster throughout this century. For example, the number of people added to the world's population in four different years of this decade were:

in 190018 million more people were added
195045 million more people
197176 million more people
199192 million more people

Why does population grow this way? Human population grows somewhat like rabbits multiplying. With more people, more kids are born. More kids grow up to be more parents. With more parents, an even greater number of kids are born, who grow up to have yet more kids, and so on. This is called "exponential growth," a "snowball effect," or "self-reinforcing feedback."

The world's industries have also been growing ever-faster. Why? First, more people mean more demand for food, houses, clothing, and goods. It takes more work and bigger industries to produce enough for the increasing numbers of people. Second, part of what industries produce is used to build new factories and machinery and farms. The more factories and machines there are, the more quickly new factories and machines can be built.

1. People need food to survive. If they were surrounded with toxic amounts of pollution, they would die. With less food and more pollution, people would die more often, and people might be born less often. This could cause the population to stop increasing and start decreasing. What factors can you think of that people need, or need to avoid, or else the death rate will increase or the birth rate may decrease? Add to this list all the factors you can think of:

2. Just as there are requirements for people to live and to be born, there are requirements to keep industry running and to build new factories, farms, stores, and offices. List as many of these factors as you can think of.

3. As the world's population increases, which factors in list (1) do you think might increase the death rate or decrease the birth rate? Why do you think these factors are likely to be important instead of others? When do you guess the factors might become important? (There are no right or wrong answers. Just decide what you think, and write it down.)

4. As the world's industries grow, which factors in list (2) do you think might decrease production of industry or decrease growth of industry? Why do you think these factors are likely to be important instead of others? When do you guess the factors might become important? (There are no right or wrong answers. Just decide what you think, and write it down.)

5. Perhaps the world could use new technology to outrace these "limits" that stop growth of population and industry. (There are no right or wrong answers. Just write down what you think about the following:)

  1. Maybe people can create inventions so that the factors in (3) do not increase the death rate or decrease the birth rate. Maybe new inventions can control the factors in (4), allowing continual industrial production and growth of industry. What new technologies might people invent to overcome the limits? How likely is it that people can create such inventions? Explain why.
  2. If new technologies overcome the limits, population and industry will then be able to grow and grow. Will continued growth create a need for more new technologies? What must the new technologies do? Does it seem likely that the technologies can be invented?

6. The world could try to solve these problems by changing lifestyles or laws instead of by developing technologies. (There are no right or wrong answers. Just write down what you think about the following:)

  1. How might people change what they do to help keep population and industry from reaching these "limits"? Make a list of your ideas.
  2. What actions might governments take to help keep population and industry from reaching these "limits"? Make a list of your ideas.

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The World3 Model and Potential Limits to Growth

In order to help think through the ideas discussed above, the book Beyond the Limits uses a computer simulation called "World3." People often make mistakes when they think about complex issues. If the assumptions of the computer simulation are correct, then the computer will make no mistakes. The results of the simulation will be logical consequences of its assumptions. Of course, we don't know which assumptions are correct, so we cannot know that the simulation gives the "right" answer. You will use the simulation to explore possible futures of Earth. You will think through how and why these futures might occur. Since no one knows the correct assumptions, you will change the simulation to try different assumptions. This way, you can explore some of Earth's possible futures.

In this process, you will find some futures that seem distressing. You will probably agree that people would rather avoid these futures. Do not be distressed! After you explore some possible futures, you will use the computer simulation to think about ways to turn possible bad futures into good ones. That's the point of the simulation: it is a tool to help you come up with ways to help make the future better.

In this section, you will explore two possible futures. Question 7 leads you through an exploration of a possible future. Question 8 has you analyze the second possible future on your own.

7. A. Start the Beyond the Limits computer program. Click on "Run the Model." Then click on "Start." The simulation will start, beginning in the year 1990. Watch how the bars change over time. For example, the population bar grows, showing that the world's population is increasing. The resources bar gets smaller, showing that the world's store of underground resources is gradually being used. Messages may appear in the bottom right corner. For example, the first message tells you that land fertility is 70% of normal. This indicates that many nutrients have leached out of the soil in many farms around the simulated world, and that on average the soil of each farm can grow only 70% as much food as it could originally grow. As you will see, this is the beginning of a food shortage that causes starvation for many people.

B. When the simulation finishes, click on the graph button on the left side. The program will draw a graph of the world's population from the year 1900 to the year 2100. The left side of the graph is for the year 1900, and as you move to the right, the year increases up to 2100. The curve on the graph shows the world's population in each year. At the very left side of the graph, in the year 1900, the population starts at 1.6 billion people. Moving to the right, you see that as the years go by, the population gets higher. It increases to 9.4 billion in the year 2040, and then it decreases because of the food shortage. The legend below the graph tells you what the population would be if it got all the way to the bottom of the graph, or if it went all the way to the top. In this case, that would mean a population of zero (no people living) or of 13 billion people.

C. Click on the messages button. A list of messages from the simulation will appear below the graph. Look through the messages by using the control (the "scroll bar") on the right side of the list. As you will see, land fertility dropped off rapidly beginning around 2030, and reached a low of 10% which lasted until 2070. A food shortage caused many people to starve beginning around 2045. To make the list go away, click on it.

D. Click on the button to pick which variables are graphed. You can choose any variables from the model. Clicking on a variable adds it to the list. From the left-hand box, click on "food" and "food per person." Then click on the graph button. Three curves will appear on the graph, showing the world's population, the total food production, and the average food available per person. The legend below the graph tells you which curve is population, food, or food per person. The total food supply keeps growing for a while, but the average food per person begins to drop off. Then the total food supply drops sharply, as does food per person. This causes starvation, and the world's population falls.

E. Why did food production decrease? It decreased because the land became less fertile, as you saw from the messages. But why did the land become less fertile?

If you have the book Beyond the Limits, turn to page 244. In any case, go to the "land fertility" diagram in the "Model Diagrams" section of the program: Click on the simulation button to return to the simulation screen. Then click on the world button to return to the main screen. Then click on "Change the Model," and (in the lower right) "Model Diagrams." Click on "Land Fertility." The diagram in the book is the same as the one in the program.

On the diagrams, the circles and rectangles represent variables, like parts in a machine. In this diagram, pipes with valves flow into and out of the box labelled "land fertility." Think of the box like a bathtub with water. Water flows into the bathtub through the left pipe, and it flows out through the right pipe. The valves determine how quickly the water flows. In this case, instead of water in a bathtub, there is land fertility in a box. Instead of water flowing in, new fertility flows in when the land regenerates. Instead of water flowing out, fertility flows away when the land is degraded. If you desire a more detailed explanation of any part of the diagram, click on the part that you want to know about.

Now that you have seen the diagram, go back to where you choose variables to graph. Click on the "Clear All" button. In the right-hand box, click on "land fertility," "land fertility regeneration," and "land fertility degradation." Click on the graph button to return to the graph. Look at the graph of land fertility. Notice how and when land fertility decreases. Why does this happen -- why does the land become less fertile? Compare the graphs of land fertility regeneration and land fertility degradation. When degradation is happening faster than regeneration, the land is becoming less fertile. Similarly, when water flows out of a bathtub faster than it flows in, the water level in the tub is going down.

Check this by graphing the following three variables together: persistent pollution index, land fertility degradation rate, and land fertility degradation. You will notice that land fertility degradation does not match exactly with the other variables. This is because when there isn't much land fertility, the land fertility can't be degraded much, because there's not much fertility left to degrade. (Similarly, if there were little water left in the tub, not much water could flow out.)

Now, try another method to investigate what happened. From the Graphs menu at the top of the screen, choose Back to return to the previous set of variables you graphed. Then choose Back once more, so that population, food, and food per person appear on the graph. Look again under the Graphs menu, and choose Click graph key for: Causes. In the menu, the check mark thereafter appears in front of Causes instead of No Action. Now, whenever you click on a variable name in the key below the graph, the program will graph the variables that directly influence, or "cause," the variable you clicked on.

Click on the word "food" in the key. The program draws a graph of arable land, land yield, land fraction harvested, and processing loss, the four variables that directly influence, or "cause," the worldwise production of food. Click again on "land yield," which dropped off at the same time when food dropped off. Now, look carefully at the resulting graph. Two variables changed and hence affected land yield: land fertility, and land yield multiplier from capital. Which one changed first? And which had the biggest effect? Notice that land fertility began to drop off even while the land yield multiplier from capital was still increasing. And indeed, the dropoff in land fertility was more severe, in percentage terms. The land yield multiplier from capital decreased by about two-thirds by the year 2100. But, in contrast, land fertility decreased by 80-90% over a span of about 30 years. Thus, it seems that land fertility, not the land yield multiplier from capital, led to the dropoff in land yield.

Before going on to investigate the causes of the dropoff in land fertility, choose Back from the Graphs menu, to go back to the previous graph. Then, again from the Graphs menu, choose Click graph key for: Info on Vars. In the menu, the check mark now appears in front of Info on Vars. You might have wondered just how the land yield is determined. Click on the words "land yield" in the graph key at the bottom of the screen. The program immediately takes you to the part of the program with the model diagrams, and it displays information about the land yield variable. As you can see from the equation shown, land yield is proportional to both land fertility and the land yield multiplier from capital. ("Proportional to" means that the equation for land yield equals land fertility and the land yield multiplier from capital multiplied by whatever else is in the equation.) Since the latter two variables get multiplied together, an 80-90% decrease in land fertility has a stronger effect on land yield than a two-thirds (roughly 66%) decrease in the land yield multiplier from capital. If you want, you can look at other variables while you are using the model diagram. Then use the Graphs menu to choose Return from Info. This takes you back to the graph you were using.

Go on investigating the causes of variables, and getting information about variables, until you are satisfied that you understand how pollution contributed to the dropoff in food. Don't forget to choose Causes from the Graphs menu, if you want to continue investigating causes of variables.

F. Now you know why the population collapsed in the simulation. High levels of pollution degraded the land's ability to produce food. Go back to where you choose variables to graph. Click on the "Clear All" button. In the right hand list, choose these four variables:

These variables show factors that affect people's lifetimes. "Crowding" of population into cities can increase lifetimes, because health care is easily available there. Crowding into cities can also decrease lifetimes, because in cities there is more pollution, and possibly more stress and more epidemics of disease. Food can increase lifetimes for people who don't have much food, because people need food to survive. Health services can increase lifetimes by preventing and curing diseases and physical ailments. In large amounts, toxic pollutants can decrease lifetimes.

Go to the graph. Notice how health services improve dramatically in the 1900s, giving people longer expected lifetimes. Notice also that lifetimes increase somewhat because more food is available. When the food shortage develops, this decreases the average person's lifetime by a large amount. Thus, you see that the food shortage shortens lifetimes, so that people die more often. The shortage is indeed the reason for the collapse in population.

G. According to the simulation model, shorter lifetimes affect the world's population in two ways: first, by increasing the death rate ("mortality"), and second, by decreasing the birth rate ("fertility"). To see this, look at the Population diagram of the model. You can get to the diagram quickly by choosing Info on Vars. from the Graphs menu and clicking on any of the variables, then clicking on the information to make it go away. The Population diagram consists of two pages; you will be on the second page (in the book Beyond the Limits, see pages 240-241). From the diagram, you can see interlinkages between variables. Life expectancy affects mortality and, in turn, deaths. (The world's population is divided into age groups, and each group has its own mortality and deaths.) On the first of the two pages of the diagram, you can also see that life expectancy (gray) affects women's ability to have children (via the "fecundity multiplier"), which in turn affects the number of births. For a deeper explanation, click on any part of the model diagrams. When you are finished, use the Graphs menu and choose Return from Info, as you did earlier. If you want, you can of course graph any of the population-related variables to see what happened to them during the simulation.

H. You've seen what happened in the simulation to the world's population, but what about the world's industry? Make a graph of "industrial output" (and, if you want, "consumer goods per person"). The world's industries rose to a vast size, but after the food crisis, the world's industrial production also dropped off. Why? Add one more variable to the graph: the "fraction of ind[ustrial] ouput alloc[ated] to agriculture." This shows how much of industrial output goes to farming, instead of to other uses. Other uses include consumer goods (e.g. cars and TVs), extraction of resources from the ground (e.g. oil and iron ore), investment in service industries, and investment in factories and machinery for manufacturing. When a lot of effort is used for farming, not so much is used to invest in industry, and the size of industry eventually decreases. (See the Industrial Ouput diagram.) If you want, you can also add "industrial capital investment" to the graph.

8. The example you did in question 7 showed one possible future. This question explores another possible future, one with a different set of problems. Many resources used by industry lie buried in the ground. How long could these resources last before they run out? Experts don't have a good answer to this question. They can't be sure what quantities of different metals, minerals, and fossil fuels are in the ground, in a form that is easy to mine or to pump out of the ground. (See pages 66-86 of the book Beyond the Limits.)

A. Go to the main screen of the program. (From the graph screen, click on the simulation button to return to the simulation screen. From there, click on the world button to return to the main screen.) Then click on "Change the Model," then on "Nonrenewable resources."

The first simulation assumed that the world has enough resources to last until the year 2200, if, from 1990 on, resources keep being used at the same pace as in 1990. What if there are only enough resources to last until the year 2100 (if, from 1990 on, resources keep being used at the same pace as in 1990)? Drag the sliding control all the way to the left, to 1 trillion resource units. (To do so, click and hold the mouse cursor on the control's button. Drag the mouse left, and the button will slide. When the button is all the way to the left, release the mouse.)

B. Return to the simulation screen. (Click on the changes table of contents button , then on the world button , then on "Run the Model.") Start the simulation. Watch what happens. Graph the results, and examine the messages from the simulation.

C. Write a summary of what happened.

D. Figure out why it happened. Write a summary that explains why.

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The World3 Model and Technology

The book Beyond the Limits uses the World3 model to consider some ways the world might use technology to try to address limits to growth. In this section of the assignment, you will try some technological strategies. You will think through what advantages and disadvantages the strategies could have, what they might achieve, and what they are unlikely to achieve.

Consider the following technologies that people could try to develop and implement. To some extent, people are working to develop these technologies.

9. Recall the simulation of question 7. You will try to develop a technology to control the problems that the world encountered in question 7's simulation.

A. What problems did the simulated world have in question 7? What technology might help resolve these problems?

B. Based on your answer to (A), change the simulation to implement one technology that the world develops. To do this: Go to the main screen of the program, then click on "Change the Model." In the table of contents, click on the appropriate technology. Set the left sliding control to its middle value. (For protection against land erosion, set the only sliding control to its middle value.)

C. When you start the simulation, what do you expect to happen? Why? Will the desired result be achieved? Write down your ideas before starting the simulation. (There are no right or wrong answers. Just write down what you expect.)

D. Start the simulation. What happens? Does it agree with what you expected? Look at graphs, messages, and model diagrams. Write a summary of what happened and why. If the results were different from what you expected, find out why and explain why.

E. Is this technology development strategy an appropriate way to ensure a better world future? Why or why not?

10. In this question, you will try to develop additional technologies to control any problems that the world encountered in the simulation of question 9. Add one new technology at a time that the world will develop. Each time you add a new technology, answer these questions:

A. What problems did the world have in the last simulation? What additional technology might help resolve these problems?

B. Turn on development of the new technology. (Leave the other settings from the last simulation. If you have quit the program, you will need to set them again.)

C. What do you expect to happen during the simulation? Why? Will you achieve the desired result? Write down your ideas before starting the simulation. (There are no right or wrong answers. Just write down what you expect.)

D. Start the simulation. What happens? Does it agree with what you expected? Look at graphs, messages, and model diagrams. Write a summary of what happened and why. If the results were different from what you expected, find out why and explain why.

After you have gone through this process a few times: What conclusions can you make? Are these conclusions valid in the real world, or only in the simulated world? Why?

(The program has detailed information about each technology that you can implement. To see the information, click on the more information button for that technology. You might also decide to change people's goals for what the technology will accomplish, or the pace at which the technology is developed. If you make these changes, then:

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The World3 Model and World Policies

Besides encouraging the development of technology, what policies might the world use to help create a better world future? The authors of Beyond the Limits have identified two such policies:

Before you go on to question 11, reset all the technologies to their original settings. That is, put the sliding controls back to the "0%" settings. Or quit the program and start it again. Quitting the program automatically resets any changes you have made.

11. In the "Change the Model" section, choose "Family planning" from the table of contents. Click on both switches to turn them "ON." The simulation model now assumes that, in 1995, every family in the world decides to have (on average) only two children. It also assumes that everyone who wants to do this can do so, because everyone has access to perfect birth control methods (family planning, contraceptives, and abstention).

A. What do you expect will happen in the simulation? Why? Will the desired result be achieved? Write down your ideas before you start the simulation. (There are no right or wrong answers. Just write down what you expect.)

B. Start the simulation. What happens? Why? Does it agree with what you expected? Look at graphs, messages, and model diagrams. Write a summary of what happened and why. If the results were different from what you expected, figure out why and explain why.

C. Is this an appropriate way for the world to achieve a better future? Why or why not?

12. Leave the family planning changes on, and make another change. In the "Change the Model" section of the program, choose "Stable industrial goals." Click on the switch to turn it "ON." (If you quit the program after doing question 11, then also turn on the switches for "Family planning.") The simulation still assumes that families will want to have (on average) two children, and that they will have the methods to have only two children. In addition, it now assumes that people decide they want a limited amount of material goods. (As indicated by the right sliding control, they want, on average, $400 worth of material goods.)

A. What do you expect to happen in the simulation? Why? Will the desired result be achieved? Write down your ideas before you start the simulation. (There are no right or wrong answers. Just write down what you expect.)

B. Start the simulation. What happens? Why? Does it agree with what you expected? Look at graphs, messages, and model diagrams. Write a summary of what happened and why. If the results were different from what you expected, figure out why and explain why.

C. Is this an appropriate way for the world to achieve a better future? Why or why not?

13. Leave on the changes from the last two questions. (If you quit the program, then turn them on again.) In addition, turn on development of all the technologies discussed on page 10 of this assignment: pollution control technology, land yield technology, land erosion controls, and resource efficiency technology. Now the simulation assumes that people do all they can to develop and implement these technologies. It assumes that families have only two children per family. And it assumes that people want only a limited amount of material goods.

A. What do you expect to happen in the simulation? Why? Will the desired result be achieved? Write down your ideas before you start the simulation. (There are no right or wrong answers. Just write down what you expect.)

B. Start the simulation. What happens? Why? Does it agree with what you expected? Look at graphs, messages, and model diagrams. (Make sure to graph life expectancy, food per person, services per person, and consumer goods per person.) Write a summary of what happened and why. If the results were different from what you expected, figure out why and explain why.

C. Is this an appropriate way for the world to achieve a better future? Why or why not?

14. Leave on the changes from the last three questions. (If you quit the program, then turn them on again.) Those questions assumed that the world made the changes starting in 1995. What would happen if the world waited until 2015 to make the changes? What if the world had made the changes in 1975? In the "Change the Model" table of contents, click on "Policy implementation year."

A. Set the policy implementation year to 2015. What do you expect to happen in the simulation? Why? Will the desired result be achieved? Write down your ideas before you start the simulation. (There are no right or wrong answers. Just write down what you expect.)

B. Start the simulation. What happens? Why? Does it agree with what you expected? Look at graphs, messages, and model diagrams. (Make sure to graph life expectancy, food per person, services per person, and consumer goods per person.) Write a summary of what happened and why. If the results were different from what you expected, figure out why and explain why.

C. Set the policy implementation year to 1975. What do you expect to happen in the simulation? Why? Will the desired result be achieved? Write down your ideas before you start the simulation. (There are no right or wrong answers. Just write down what you expect.)

D. Start the simulation. What happens? Why? Does it agree with what you expected? Look at graphs, messages, and model diagrams. (Make sure to graph life expectancy, food per person, services per person, and consumer goods per person.) Write a summary of what happened and why. If the results were different from what you expected, figure out why and explain why.

E. What conclusions can you draw from comparing policies implemented in 1975, 1995, and 2015? Do you think that your conclusions from these simulations are appropriate for the real world? Why or why not?

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The World3 Model's Sensitivity to Assumptions

The simulations you have done reflect futures that could happen, given that the people of the world make certain choices or take certain actions. But remember, the simulation doesn't know for sure what will happen, even if you tell it what choices and actions people will use.

15. How would the simulation come out differently if certain assumptions in the model were different? Think about this on your own and with your friends. In some cases, you can use the simulation to test this out. For example, nobody knows how many resources the world has. Change the amount of nonrenewable resources and use the simulation to check how this could affect what policies the world should use to ensure a good future.

16. The Sensitivity Analysis section of the program lets you randomly change many assumptions at once, to see what difference this makes. For example, you might change all model parameters by random amounts averaging plus or minus 25%. This is a modest change in parameters. Do the conclusions of the World3 model hold up under such changes? This section of the program runs the model many times, keeping track of the results. You can analyze the range of different outcomes of the model, the range of outcomes that would result given different policies, and which parameters make a big difference in the results when one parameter at a time is changed. If you have a fast computer, set up your own policy suggestions and analyze policy effects.

17. Perhaps the assumptions of the model are fairly close to the truth, and people need to act now with the policies you've tried out. More likely, many assumptions are wrong, and wrong in ways that would require rebuilding the underlying structure of the model rather than just changing the values of parameters. Perhaps, then, some conclusions based on the model might be wrong. Perhaps not all the recommended policies are necessary. What policies are most important? Why? Is there any way to know which policies are necessary? Do we need to use all of the policies to ensure a good future?

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Strategies for the Future

In this workbook, you've explored possible world futures using the World3 computer simulation. You've used the simulation to think about ways people could try to build a good future. In this section, you step back from the computer. Discuss these questions with your classmates and friends. [Teachers may want to organize a discussion for the whole class.]

18. The following are key concepts from the book Beyond the Limits. Make sure you understand each term. Discuss what the terms mean, and how these concepts are used in Beyond the Limits. (Page numbers refer to the book.)

19. What can people and governments do to help build a better future for the world? What should they do? What will they do? How can you lead people and governments to create a better future? What do you personally want to do to help create a better future?

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Copyright ©1992-1997 by Kenneth L. Simons.
Revised 8 September 1997.